Patent GB-829126-A (GB)
Title: An improved method of and apparatus for testing internal combustion engines
Filed: 1956-08-31
Abstract: 829,126. Testing internal-combustion engines. GENERAL MOTORS CORPORATION. Aug. 31, 1956 [Aug. 31, 1955], No. 26651/56. Class 40 (1). Apparatus for measuring the pressure existing within a cylinder of an internal-combustion engine at a particular engine crank angle comprises means for developing a timing mark signal at a predetermined crank angle position, a pressure-sensitive switch 12, one side of the diaphragm of which is exposed to cylinder pressure and the other side of which is exposed to an adjustable source of balance pressure, operated when the engine cylinder pressure on one side of the diaphragm attains the balance pressure on the other side, and means for comparing the times of the timing mark signal and the operation of switch 12. General, with reference to Fig. 1.-Component 12 (as shown in Fig. la) changes from the non- conducting to the conducting position as the pressure in the cylinder increases from below to above the balancing pressure and becomes non-conducting again as the pressure falls below this point. Hence square waveform H, Fig. 5, is produced in line 50 and is fed into the coincidence detector 30. The timing mark signal is produced capacitively by the approach of a tooth on a disc 56 driven by the engine to a rod 54, the position of which is adjusted by a motor and shown on a scale 66. The position is also transmitted to a recording system by means of position indicator transducer 26. Coincidence detector circuit.-Waveform A, Fig. 5, appears at the output of stage 1 of the coincidence detector shown in Fig. 3 as a result of each impulse on line 62 from the timing signal producer and waveform G at the output stage of valve 5. Signals G and H are mixed in valve 6 in such a manner that if and only if they occur together a pulse is produced in the output stage of valve 6. This pulse indicated by I is used to trigger a unistable multi-vibrator whose output is fed through a cathode follower to the error detector 32. The amplitude of the square wave output from this multi-vibrator is varied by variable resistor 132 and this may be used to allow for variation due to running the engine at different speeds. The frequency of the square pulses is dependent upon the rate of coincidence. The error detector produces a signal whose magnitude is a measure of the time average of these square pulses and hence is a measure of the rate of coincidence. Servo-control and operation.-In operation the apparatus is adjusted so that the error detector gives no signal if the rate of coincidence is about 50%. The error detector energizes a servo-amplifier 34 and a servomotor 36 which regulates regulator 16 in such a way that if the . coincidence rate is above 50% regulator 16 increases the pressure in 12 and if the coincidence rate is below 50% the pressure in 12 is reduced. The apparatus may be used to make discrete measurements or to make continuous measurements. The apparatus indicated at 40 may be any two axis xy function plotter with positions controlled by position indicator transducer 26 and with pen movements controlled by a signal from the pressure transducer 18.